Quantum-chemical study of the relative stability of conformers of 1,4-dihydropyrazine and 1,4-dihydro-1,4-diphosphinine

Spatial and electronic structure of the molecules of 1,4-dihydropyrazine and 1,4-dihydro-1,4-dihydrophosphinine was studied by the non-empirical method G2. The boat conformation with the syn-orientation of the lone electron pairs was shown to be the most preferable form for both molecules.     

Looking glass inhibitors: synthesis of a potent naringinase inhibitor l-DIM [1,4-dideoxy-1,4-imino-l-mannitol], the enantiomer of DIM [1,4-dideoxy-1,4-imino-d-mannitol] a potent α-d-mannosidase inhibitor

The synthesis of l-DIM [1,4-dideoxy-1,4-imino-l-mannitol] and of 1,4-imino-d-glycero-l-talo-heptitol from d-glycero-d-gulo-heptono-1,4-lactone depends on the use of pentan-3-one to form two five ring ketals as described by Burke, rather than the formation of one five ring and one six ring ketal formed with acetone. l-DIM, the enantiomer of the potent α-d-mannosidase inhibitor DIM [1,4-dideoxy-1,4-imino-d-mannitol] is a good inhibitor of naringinase (an α-l-rhamnosidase) with a K_i of 3.63 μM. 1,4-Imino-d-glycero-l-talo-heptitol is a moderate inhibitor of naringinase.     

Reactions of palladium (II) chloride with 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene and 1,4-DI(p-methoxyphenyl)-2,3-dimethyl- 1,4 - diazabutadiene

The reactions of palladium(II) chloride with 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene and 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene are described. With 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene diimine fission is produced, giving rise to a product identified by elemental analysis, IR and Raman spectra, and X-ray diffraction, as trans-dichlorobis(aniline) palladium(II). The complex is soluble in dimethylformamide and crystallizes with two molecules of solvent. The substance crystallizes in the monoclinic space group P2₁/n. The X-ray data were refined to R = 0.047 and R_w = 0.046. Final distances are PdN = 2.060(5)Åand PdC1 = 2.299(2)Å. There are two bifurcated intermolecular NH ... C1 and CH... C1 hydrogen bonds which, together with one more intermolecular hydrogen bond NH... O, are responsible for the packing of the molecules. However, when 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene was treated with palladium chloride under the same conditions cis - dichloro - 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene was formed, as deduced from elemental analysis, and IR and Raman spectra.     

Comparison of preparation methods of N-arylsulfinyl-1,4-benzoquinone monoimines

Advantages and shortcomings were discussed of three procedures for preparation N-arylsulfinyl-1,4-benzoquinone imines: the reaction of arenesulfenyl chlorides with 1,4-benzoquinone oximes, the oxidation of N-arylthio-1,4-benzoquinone imines, and the reaction of arylsulfinyl chlorides with p-aminophenols followed by oxidation. A series of new N-arylsulfinyl-1,4-benzoquinone imines was obtained.     

Synthesis of 2,5-diethynyl substituted oxepins from trans-1,4-diethynylcyclohexa-2,5-diene-1,4-diols

Reaction of trans-1,4-bis(trimethylsilylethynyl)cyclohexa-2,5-diene-1,4-diol with n-BuLi followed by methanesulfonyl chloride resulted in the formation of a dark red solid, which was identified as 2,5-bis(trimethylsilylethynyl)oxepin. Deprotection of the silyl groups resulted in the formation of 2,5-diethynyloxepin, a red, shock sensitive solid. Reaction of a differentially substituted cyclohexa-2,5-diene-1,4-diol gave a mixture of 2,5-diethynyl substituted oxepins.     

Reaction of N-arylcarbamoyl-1,4-benzoquinone imines with sodium azide

N-Arylcarbamoyl-1,4-benzoquinone imines reacted with sodium azide in completely regioselective fashion according to the 1,4-addition pattern with formation of 1-(3-azido-4-hydroxyphenyl)-3-arylureas. The reaction of N-arylcarbamoyl-2,6-dichloro-3,5-dimethyl-1,4-benzoquinone imines with sodium azide afforded N-arylcarbamoyl-2,6-diazido-3,5-dimethyl-1,4-benzoquinone imines as a result of nucleophilic substitution of the chlorine atoms.     

Reactivity of N-arylsulfonyl-1,4-benzoquinone imines. Reaction with hydrazoic acid

N-Arylsulfonyl-2-halo-1,4-benzoquinone imines react with hydrazoic acid in boiling acetic acid via two pathways: the 1,4-addition and nucleophilic replacement of the halogen atom by an azido group, followed by the 1,4-addition of HN₃. In the reaction of N-arylsulfonyl-2,6-dihalo-1,4-benzoquinone imines with hydrazoic acid, both halogen atoms are replaced by azido groups, while N-p-tolylsulfonyl-2-methyl-1,4-benzoquinone imine takes up HN₃ molecule according to the 1,4-addition pattern.     

Resolution of C2-symmetric 2,3-diphenylbutane-1,4-diol and purification of diastereomeric 1,4-diphenylbutane-1,4-diol using (S)-proline and boric acid

Racemic 2,3-diphenylbutane-1,4-diol (±)-1 is resolved to obtain the corresponding (R,R)-isomer in 98% e.e. through reaction with (S)-proline and boric acid. Partially resolved (R,R)-(−)-1 and (S,S)-(+)-1 have been enriched to obtain samples of 95 and 97% e.e. through reaction with (S)-proline and boric acid. Diastereomeric 1,4-diphenylbutane-1,4-diol 2 has been purified to obtain the (R,R)-isomer in 98% e.e. using (S)-proline and boric acid.     

Electrolytic reduction of 2-butyne-1,4-diol as a route to trans-2-butene-1,4-diol

The effect of the cathode material on the electrochemical transformations of 2-butyne-1,4-diol at atmospheric pressure was studied by chromatographic analysis. The optimal parameters of the selective synthesis of trans-2-butene-1,4-diol were determined.     

Synthesis and crystal structure of cyclopentadienyl(1,4-dimethyl-1,4-dibora-2,5-cyclohexadiene)cobalt

The synthesis of the organometallic derivative cyclopentadienyl(1,4-dimethyl-1,4-diboracyclohexa-2,5-diene)cobalt is described. This complex, [(CH₃BC₄H₄BCH₃)Co(η-C₅H₅)], forms red-oranged monoclinic crystals, space group P2₁/a with Z = 4 in a unit cell of dimensions a 11.362(7), b, 7.467(7), c 13.290(12) Å, β 103.76(6)°. The structure has been elucidated by heavy-atom methods from 1732 reflections (I > 2σ(I)) measured on a Syntex P2₁ four-circle diffractometer and refined to R = 0.055. In the coordination complex all six atoms of the cyclohexadiene ring are within bonding distance of the metal atom, but the two boron atoms bend away from the metal atom, and the ring elongates slightly in the B---B direction. As a standard of comparison the known geometry of the free ligand [1,4-difluoro-1,4-dibora-2,3,5,6-tetramethylcyclohexa-2,5-diene] is used. The terminal methyl groups on the boron atoms, by contrast, bend slightly back towards the metal atom. The cyclopentadienyl ring remains planar but is positionally disordered.     

4,4-Dimethyl-1,4-thiasilinane and Its S-Functional Derivatives

Synthetic approaches to 4,4-dimethyl-1,4-thiasilinane and its S-functional derivatives, 4,4-dimethyl-1,4-thiasilinane S-oxide, 4,4-dimethyl-1,4-thiasilinane S,S-dioxide, 4,4-dimethyl- 1-(phenylsulfonylimino)-1,4-thiasilinane, and 1,4,4-trimethyl-1,4-thiasilinan-1-ylium iodide, were studied. The S-functional derivatives of 4,4-dimethyl-4-thiasilinane, unlike 3,3-dimethyl-3-thiasilinane, are hydrolytically stable.     

Istope effects in aromatization of 1,4-dihydrobenzene and 1,4-dihydronaphthalene with quinones

Aromatization of 1,4-dihydronaphthalene with 2,3-dichloro-5,6-p-benzoquinone or chloranil is accompanied with kinetic isotope effects of 9.9 and 8.0 respectively.     

The conformation and vibrational spectra of trans-1,4-dihalocyclohexanes: Part III. trans-1,4-Diiodo-, trans-1,4-bromoiodo- and trans-1,4-dibromocyclohexane

The IR spectra of trans-1,4-diiodo- and trans-1,4-bromoiodocyclohexane as solutes in various solvents, as pellets and as solids under high pressure are recorded in the region 4000–30 cm^?1. Additional spectra of the melts, amorphous and annealed crystalline solids at 90 K and dichroic spectra of oriented crystals are recorded above 200 cm^?1. Raman spectra of the amorphous and annealed solids at 90 K and as solutes in various solvents, are obtained, including polarization measurements. IR and Raman spectra of trans-1,4-di-bromocyclohexane in the temperature range 90–250 K are recorded. Equilibrium mixtures of ee and aa conformers of the title compounds are observed in solution, in the melts and in the amorphous solid at 90 K. The ee conformer only is present in the stable crystal, while the aa conformer predominates in apparently metastable crystals annealed to ca. 205 K. The concentration of the aa conformer increases under high pressure (50 kbar). Fundamental frequencies for both ee and aa conformers are assigned. A normal coordinate analysis is carried out, and the force Fields adjusted to nine halogenated cyclohexanes using the overlay technique.     

Facile synthesis of substituted dihydro-1,4-dithiins and -1,4-dithiepins from α-oxo ketene cyclic dithioacetals

A novel and facile synthesis of substituted 2,3-dihydro-1,4-dithiins and 6,7-dihydro-5H-1,4-dithiepins based on the reactions of α-bromo/hydroxy ketones with α-oxo ketene cyclic dithioacetals has been developed. A general mechanism for the reactions is proposed.     

Reaction of N-arylsulfonyl-2(3)-arylsulfonylamino-substituted 1,4-benzoquinonimines with sodium arylsulfinates

N-Arylsulfonyl-3-arylsulfonylamino-substituted 1,4-benzoquinonimine reacts with sodium arylsulfinates regiospecifically along 1,4-addition scheme; N-tosyl-2-(tosylamino)-substituted 1,4-benzoquinonimine regioselectively affords products of 1,4- and 6,3-addition with the latter prevailing. Arylsulfinate anion enters predominantly in the para-position with respect to the ArSO₂NH group.     

Direct synthesis of 4,4-disubstituted N-silyl-1,4-dihydropyridines

An unprecedented method for the preparation of 4,4-disubstituted 1,4-dihydropyridines is presented. It is based on the trapping reaction of 4-substitued N-silylpyridinium ions. When performed with dialkylmagnesium reagents, such as iPr₂Mg, silyl protected 4,4-disubstituted 1,4-dihydropyridines were obtained in up to quantitative yields. High 1,4-selectivity was found for sterically demanding nucleophiles, whereas small nucleophiles (Me₂Mg) tend to yield 1,2-addition-products. Grignard, dialkylzinc and organocopper reagents were found to give either no addition products or less favorable results. Reduction of the obtained 1,4-dihydropyridine with NaCNBH₃ in the presence of HCl, followed by treatment with tert-butyl dicarbonate provided the corresponding N-Boc protected piperidines with high yields.     

Interaction of a lithiated nitronyl nitroxide with polyfluorinated 1,4-naphthoquinones

A 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl lithium derivative was found to react with 2-methoxypentafluoro-1,4-naphthoquinone to form a product of addition at the carbonyl function: radical 2-(3,5,6,7,8-pentafluoro-1-hydroxy-2-methoxy-4-oxo-1,4-dihydronaphthalen-1-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl. The yield of the addition product increased with temperature and reached 84% at 0?°C. The reaction of the lithium derivative with hexafluoro-1,4-naphthoquinone gave rise to a product of addition at both carbonyl groups, namely, nitronyl nitroxide diradical 2,3,5,6,7,8-hexafluoro-1,4-bis(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazole-2-yl)-1,4-dihydronaphthalene-1,4-diol in a 16% yield. The structures of both mono- and diradical were solved by X-ray diffraction analysis, which revealed formation of an intramolecular H-bond between the OH group and nitroxide oxygen. According to electron paramagnetic resonance (EPR) spectroscopy, the obtained mono- and dinitroxide are prone to spontaneous deoxygenation in a toluene solution to give corresponding iminonitroxides. In water, they are much more stable.     

A general synthesis of N-substituted 1,4-benzoxazine- and 1,4-benzothiazine-2-carboxylates via copper-catalyzed intramolecular amination of arylbromides

Starting from ortho-bromosubstituted phenoxyacetates or (phenythio)acetates and primary amines, various N-substituted 4H-1,4-benzoxazine- and 4H-1,4-benzothiazine-2-carboxylates were synthesized in moderate to high yields by using a Cu(I)-catalyzed Ullmann-type cyclization as a key step. The method is simple to operate, tolerates many functional groups and does not require any additives.     

Vibrational analysis of 1,4-dibromopentane

Infrared and Raman spectra have been obtained for 1,4-dibromopentane and interpreted with the aid of normal coordinate calculations. It is concluded that all six conformers resulting from rotation about the C₁-C₂ and C₃-C₄ bonds probably exist in the neat liquid and amorphous solid, and that the compound crystallizes in the P_HS_HH conformer that has the two bromine atoms on opposite sides of the plane of carbon atoms. The compound therefore behaves like 1,3-dibromopropane and 1,4-dibromobutane.     

Cyclization of 2-chloro-3-(1,4-oxocyclohexa-2,5-dienylideneamino)-1,4-dihydronaphthalene-1,4-diones into 6-chloro-10,12a-dihydroxy-7H,12aH-benzo[c]phenoxazin-5-ones

2-Chloro-3-(4-oxocyclohexa-2,5-dienylideneamino)-1,4-dihydronaphthalene-1,4-diones maintained in the conc. sulfuric acid undergo cyclization affording in a high yield 6-chloro-10,12a-dihydroqи-7H,12aH-benzo[c]phenoxazin-5-ones whose structure is proved by XRD analysis.